This invention relates to cementing valve apparatus and particularly to differential fill valve apparatus for use in earth wells and the like.
When a string of casing is to be run into an earth well, the casing may be open ended at the bottom whereby the drilling mud or other pumpable material in the well simply fills the casing as the string is lowered into it.
On the other hand, the bottom part of the casing string may be closed, keeping the casing somewhat buoyant as the string is lowered through pumpable material.
When the bottom part of the casing is closed, the resulting buoyancy relieves some of the strain on the drilling rig, but sometimes too much buoyancy occurs.